added optional descriptions to most parts of the activity json schema
start of support for BricLayer brix-topic dynamic value

Brix classes that support this need to implement a getEventTopic static method.

I've implemented that static method on a few Brix classes:
Callouts
Carousel
ImageViewer
LabelGroup
MultipleChoiceQuestion
Implement getBricTopic

unit tests are still needed.
Update d3 to version 3.3.7

https://github.com/mbostock/d3/releases/tag/v3.3.7
unit test BricWorks.getBricTopic
BricLayer dynamic value tests including for the new brix-topic type.
convert tabs to spaces, no other changes.
activity schema dynamicValue now references all the defined types
Add quotes around property names that didn't have them in the activity config
changed tabs to spaces
Merge pull request #103 from lbondaryk/350-Hilight-mortar

350 hilight mortar (briclayer support for brix-topic dynamic value)